You have a website. You need email that matches your website.
Let’s do this for Free and then use your Gmail account to send and receive it. All email in one inbox and still portraying the business image.
Here is the documentation from Mailgun:
The instructions above are good but there are more for the technical aspects and not how to do it.
I found this great article that give you a nice step-by-step for setting up Mailgun for your domain by Renzo Lucioni
Here is another article by VRC Works
When I setup a Side Hustle Site for you I will do the mailgun setup for you.
Do you have to use Mailgun?
No, you can use the email boxes or mail forwarding with your domain registrar. BUT, if I host your site and we also decide to use CloudFlare for DNS then we have have to look towards another solution.
The best solution in my opinion is to use Google Apps